diff --git a/ch01.asciidoc b/ch01.asciidoc
index 8b3f579d..a52947af 100644
--- a/ch01.asciidoc
+++ b/ch01.asciidoc
@@ -45,7 +45,7 @@ When cryptography started becoming more broadly available and understood in the
 
 === History of Bitcoin
 
-((("getting started", "bitcoin history")))((("Nakamoto, Satoshi")))((("distributed computing", "bitcoin history")))Bitcoin was invented in 2008 with the publication of a paper titled "Bitcoin: A Peer-to-Peer Electronic Cash System,"footnote:["Bitcoin: A Peer-to-Peer Electronic Cash System," Satoshi Nakamoto (https://bitcoin.org/bitcoin.pdf)] written under the alias of Satoshi Nakamoto. Nakamoto combined several prior inventions such as b-money and HashCash to create a completely decentralized electronic cash system that does not rely on a central authority for currency issuance or settlement and validation of transactions. ((("Proof-of-Work algorithm")))((("decentralized systems", "consensus in")))((("consensus", "Proof-of-Work algorithm")))The key innovation was to use a distributed computation system (called a "Proof-of-Work" algorithm) to conduct a global "election" every 10 minutes, allowing the decentralized network to arrive at _consensus_ about the state of transactions. This elegantly solves the issue of double-spend where a single currency unit can be spent twice. Previously, the double-spend problem was a weakness of digital currency and was addressed by clearing all transactions through a central clearinghouse.
+((("getting started", "bitcoin history")))((("Nakamoto, Satoshi")))((("distributed computing", "bitcoin history")))Bitcoin was invented in 2008 with the publication of a paper titled "Bitcoin: A Peer-to-Peer Electronic Cash System,"footnote:["Bitcoin: A Peer-to-Peer Electronic Cash System," Satoshi Nakamoto (https://bitcoin.org/bitcoin.pdf)] written under the alias of Satoshi Nakamoto. Nakamoto combined several prior inventions such as b-money and HashCash to create a completely decentralized electronic cash system that does not rely on a central authority for currency issuance or settlement and validation of transactions. ((("Proof-of-Work algorithm")))((("decentralized systems", "consensus in")))((("consensus", "Proof-of-Work algorithm")))The key innovation was to use a distributed computation system (called a "Proof-of-Work" algorithm) to conduct a global "election" every 10 minutes, allowing the decentralized network to arrive at _consensus_ about the state of transactions. ((("double-spend problem")))This elegantly solves the issue of double-spend where a single currency unit can be spent twice. Previously, the double-spend problem was a weakness of digital currency and was addressed by clearing all transactions through a central clearinghouse.
 
 The bitcoin network started in 2009, based on a reference implementation published by Nakamoto and since revised by many other programmers. The implementation of the Proof-of-Work algorithm (mining) that provides security and resilience for bitcoin has increased in power exponentially, and now exceeds the combined processing power of the world's top super-computers. Bitcoin's total market value is estimated at between $10 billion and $15 billion US dollars, depending on the bitcoin-to-dollar exchange rate. The largest transaction processed so far by the network was $150 million US dollars, transmitted instantly and processed without any fees.